1. Field of the Invention
The present invention generally relates to the removal of a die from a substrate and, more particularly, to using a bimetal removal apparatus to remove a die from a substrate.
2. Description of the Related Art
Advanced chips or die, such as, for example, high performance chips with increased logic complexity, require testing before the chips are assembled into final products. Conventional chip testing uses temporary electronic packages that allow all of the chip's input/output connectors to be simultaneously available for electronic testing. The chip's connectors are attached to the temporary electronic package's substrate via a controlled collapse chip connection (also known as C4), e.g., C4 solder balls.
Once the chip testing is completed, the chip must be separated from the temporary electronic testing package so that the C4's remain in tact and connected to the chip. This must be done without damaging the chip and, more specifically, without damaging the BLM (i.e., the solder ball limiting metallurgy) of each of the chip's connectors. The BLM defines the size and area of the soldered connection, limits the flow of the solder ball to the desired area, and provides adhesion and contact to the chip wiring. If the BLM of any connector is damaged during separation, the chip is considered damaged and/or unusable. Similarly, if, upon separation, the solder separates from the chip side connector (as opposed to the substrate side), the connector (and therefore the chip) is unusable.
The two types of conventional separating processes include cold shear, which is done at room temperature, and warm shear, done at an elevated temperature. Each of these processes shear the chip from a testing substrate by the application of static shearing force. In the case of cold shear, a direct and constant force is applied to the side of the chip. This operation is conventionally done as a bench top operation. In the case of warm shear, the C4 (i.e., the soldered connection) is heated (i.e., via a belt furnace). This limits the various options for applying shear force to stand alone fixtures that can pass through a belt furnace. To insure an even distribution of heat across the C4 array and substrate, fixture size and mass is also limited. Conventionally, springs are utilized to generate the shearing force. More specifically, the substrate is anchored in the fixture, the springs are compressed and the shear force is transferred to the C4 array. The fixture, loaded with product, is then heated and as the C4 (i.e., the soldered connection) is heated and softens (i.e., via a belt furnace), the chip shears away from the substrate.
However, the application of shearing force to the chip and the C4 ball array prior to the desired temperature often times results in damage to the BLM. Advanced chip testing requires 100% module yield. However, conventional separation techniques cannot consistently produce 100% module yield. The amount of damage and the number of damaged chips increases for example, the greater the number of connectors, the smaller the size of the connection pads, and/or the less uniform the connection material (as opposed to conventional solder), such as with advanced chips such as those with 5,000 or greater I/O and with interconnections on the order of 0.004″ on 0.008″ centers.
Conventional chip detach methods such as those disclosed in U.S. Pat. No. 5,553,766, entitled “In-situ Device Removal For Multi-chip Modules,” U.S. Pat. No. 5,779,133, entitled “In-situ Device Removal For Multi-chip Modules,” (a Divisional of '766), and U.S. Pat. No. 6,216,937, entitled “Process And Apparatus To Remove Closely Spaced Chips On A Multi-chip Module,” (each incorporated herein by reference) teach the use of bimetallic disk or memory device to pull the chip from a package once the assembly reaches the solder softening point or, in other words, gripping and exerting a tensile force on the chip at different operating temperatures relative to the solder ball melting points. However, these detach techniques of gripping and pulling cannot guarantee that the BLM will not be damaged and/or that the solder balls will stay on the chip's connectors during and after chip detachment.